This is something I haven't seen before and am not sure how to handle. A warehouse has a 600a or 800a distribution panel (not sure which) feeding a 125a, 3-phase, 208v. branch circuit panel. When they plug in a small space heater in an office,the 125a main in the dist.pnl. trips after about 10 minutes,(the 20 a. breaker for the office cir. and the 125a. main in the branch cir. panel do not trip). The load on the cir. is 12a. with the heater going and there is very little load on the 125a. breaker (like 40a. on C ph.). The dist.pnl. is a GE Spectra series,the branch pnl. is square D QO. The breaker has the adjustable trip aic and I've gotten prices ranging from $1000 to $1900 for it. I don't want to just replace the breaker and find out that is not the problem. Thanks.
I had an emergency call at a large office building, dark and stormy night, The main was tripped. I turned off all the breakers and reset the 2000 Amp (I think) main. Then turned on each breaker one at a time till it tripped again. I got everything on except the one 200amp panel. Turned out an A/C unit had a ground fault. Check the heater. Good luck Rod
Re: distribution breaker trips branch circuit doesn't#48562 02/15/0508:10 PM02/15/0508:10 PM
Another thing to check for is loose connections at the breaker, including the connection to the distribution busbar. Heat from a loose connection can trip a breaker.
If you find no loose connections, listen for sizzling or crackling sounds in the breaker which would indicate internal connections going bad. Try placing the tip of a large screwdriver against the breaker case & then place your ear against the end.
Few things are harder to put up with than the annoyance of a good example.
Re: distribution breaker trips branch circuit doesn't#48563 02/15/0508:15 PM02/15/0508:15 PM
Thanks for the replies. I did not suspect a short in the heater since it worked fine when plugged in to a circuit fed from a different panel but maybe a low level short? I will definately check for a loose connection today. Don thanks for the link--very helpful I could not find it on GEs website yesterday. The trip unit plug sounds like a good place to start ($106).
Re: distribution breaker trips branch circuit doesn't#48565 02/17/0509:35 PM02/17/0509:35 PM
The last time I saw this was a service that was within 25 feet of the Utility Co transformer. The AIC rating was so high that short in a 20A circuit would trip the main even with the adjustable main overload cranked.
Re: distribution breaker trips branch circuit doesn't#48566 02/18/0511:15 AM02/18/0511:15 AM
The AIC (amps interrupting capability)rating of a device has nothing to due with it's trip curve. However, the available short circuit amps (SCA) does affect the amount of fault current that flows which may cause upstream devices to operate.
I agree with the comments about the trip unit rather than the entire breaker.